Control means for air blast circuit breakers



July 21, 1964 H. FORWALD 3,141,942

CONTROL MEANS FOR AIR BLAST CIRCUIT BREAKERS Filed Aug. 1, 1960 3Sheets-Sheet 1 I /Z% I 2 L 22 INV EN TOR.

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CONTROL MEANS FOR AIR BLAST cmcurr BREAKERS Filed Aug. 1, 1960 Q 3Sheets-Sheet 2 July 21, 1964 v H. FORWALD 3,141,942

CONTROL MEANS FOR AIR BLAST CIRCUIT BREAKERS Filed Aug. 1, 1960 3Sheets-Sheet 3 705 I16 I06 I76 1/4 Z- f z5 4..

i x w INVENTOR. AMI/(0N Folk/410 United States Patent 3,141,942 CUNTRQLMEANS FOR AER BLAST CIRCUIT BREAKERS Haakon For-Wald, Ludvika, Sweden,assignor to Allmanna Svenska Elektrislra Aktieholaget, Vasteras, Sweden,a corporation of Sweden Filed Aug. 1, 19nd, Ser. No. 46,659 Claimspriority, application Sweden May 7, 1960 6 Claims. (Cl. 2(i0148) Thisinvention relates to air blast circuit breakers and more specificallyrelates to a control for a high pressure air cut-off means for normallyisolating a source of compressed air from an interrupter structure andits support so that compressed air will not be lost in the event of aleak in the interrupter or its support.

Air blast circuit breakers are well known in the art, wherein compressedair is supplied to an interrupter or are extinguishing chamber through asupport pillar insulator. The insulators are filled with compressed airwhen the contacts of the interrupter are in the open as well as theclosed position. During an opening operation the compressed air withinthe insulator and are extinguishing chamber supplies an air blast forextinguishing the arc drawn by the contacts.

If there is a leak somewhere within the insulator or are extinguishingchamber, the high pressure air required for the blast will be lost.Furthermore, if the contacts are open, the loss of pressure may cause anunintentional closing of the contacts. Where a plurality of individualinterrupters are mounted on separate pillar insulators with a commonsupply of high pressure air, it is clear that a fault in any portion ofthe high pressure system will permit reclosing of all of theinterrupters.

In order to prevent loss of high pressure gas and unintentionalreclosing, the individual pillar insulators have heretofore beenprovided each with its individual reservoir of high pressure gas, thesereservoirs being connected to the main source of high pressure throughsmall orifices. Thus, if there is a break in one of the pillarinsulators, the main pressure source, and the reservoirs, for the otherpillar insulators, drain through the restrictive orifices wherebyrepairs can be effective before a serious pressure loss occurs.

This system is subject to the disadvantage that, after contact operationand air blast, the compressed air for the various reservoirs is drainedand is not quickly replen ished. If the pressure level falls too low, itis possible for the contacts to reclose unintentionally, so that theorifices for this reason should preferably be large. On the other hand,for the orifice to be operable to isolate the main pressure source froma broken pillar insulator, it is preferably small.

In accordance with the present invention, the orifice is (ept smallwhile quick replenishing of high pressure gas after contact operation isprovided. Thus, the orifice is placed in a valve type structure which ismomentarily opened during blast operation and is thereafter closed. Thispermits a quick replenishing of high pressure gas to the individualreservoirs and, if one of the insulators is broken, the high pressuresource is directly exposed to this break for only the very short timethat the valve is open.

However, the above described arrangement is hardly suitable when fillingthe circuit breaker with compressed air at the time of initially puttingit into service, because when the restrictive orifices are opened theoutlet valves of the interrupting chambers are also opened so that alarge amount of the air supplied is conducted directly out to the openair. To avoid this disadvantage the present invention provides meanswhereby the restrictive orifices of such a system may be controllablyopened during times other than the contact operation time so that, forexample, the auxiliary pressure supplies may be supplied at any desiredtime other than contact operating time and when the unit is initiallyplaced in service.

Accordingly, a primary object of this invention is to provide a novelpressure supply control system for air blast circuit breakers whereineach of a plurality of series connected interrupters are pneumaticallyisolated from one another.

Another object of this invention is to isolate pneumatically a number ofseries connected interrupters from one another and from a main source ofhigh pressure air so that a leak in any one of the interrupter systemswill not cause a drain of high pressure air from either the remainingsystems or the main source of supply.

Another object of this invention is to provide a restrictive orificebetween a compressed air reservoir or chamber which supplies the airblast for an interrupter chamher and the main source of high pressureair wherein the orifice is temporarily opened during the openingoperation of the interrupter to replenish the supply of air in thecompressed air reservoir.

A further object of this invention is to provide a novel control systemfor normally isolated auxiliary pressure supplies of a gas blast circuitbreaker wherein the restrictive orifice may be defeated at any desiredtime.

Other objects of this invention will become apparent from the followingdescription when taken in connection with the drawings in which:

FIGURE 1 shows a side view of one pole of a circuit breaker having aplurality of series connected interrupters, and with a first embodimentof a restricted orifice defeating means for auxiliary pressure chamberswhich are normally-isolated from one another.

FIGURE 2 shows a second embodiment of the invention.

FIGURE 3 shows in part an interrupter with a pair of cooperatingcontacts in the closed position.

FIGURE 4 shows the same interrupter as FIGURE 3, with the contacts inthe open position.

Referring now to FIGURE 1, the pole of the circuit breaker shown in thisfigure includes a first terminal 1 and a second terminal 2 which areconnected in series with the four interrupting chambers or interrupters3, 4, 5 and 6, which may be of the type shown in FIGURES 3 and 4. Eachof interrupters 3, 4, 5 and 6 are mounted on hollow pillar insulators 7,8, 9 and 10 respectively which are in turn mounted on compressed airreservoirs or containers 11, 12, 13 and 14 respectively which are inpneumatic communication with the interior of their respective pillarinsulators and interrupter chambers. Each of compressed air containers11 to 14 communicate with conduit 15 which is connected through valve 61to a main source of high pressure air (not shown) as through passages16, 17, 18 and 19 respectively. The main conduit 15 is provided with aplurality of cylindrical open ings 20, 21, 22 and 23 which receivepistons 24, 25, 26 and 27 respectively. Each of these pistons thencarries a projecting nozzle such as nozzles 28, 29, 30 and 31 which seatin the openings of passages 16, 17, 18 and 19 respectively. Each ofnozzles 28 to 31 are provided with orifices or controlled leaks 32, 33,34 and 35 respectively where these controlled leaks are small enough toexert a substantial resistance to the flow of gas therethrough. Each ofnozzles 28 to 31 are normally biased upwardly to restrict theirrespective orifices by biasing springs 36, 37, 38 and 39 respectively.

With the structure shown to this point, a relatively high pressure ismaintained within containers 11 to 14, their individual pillarinsulators 7 to 10 and their individual interrupter structures 3 to 6.This high pressure is used for obtaining a gas blast which extinguishesan arc 3 drawn by the contact within the arc extinguishers as has beendescribed in connection with FIGURES 3 and 4.

In order to initiate operation of the contacts of the arc extinguishers,a control air system which includes feeders 40, 41, 42 and 43 of controlconduit 44 are connected to the gas pressure responsive means within theinterrupters 3 to 6. Thus, assuming that a relatively high pressureprevails in the interrupters 3 to 6, supplied through pillar insulators7 to 10 by compressed air, so long as a relatively high pressure isapplied to feeder conduits 4-9 to 43 respectively, the interruptercontacts will be moved to and retained in an open position. The openingwill take place under the influence of a blast of air contained withincontainers 11 to 14.

The contacts of the interrupters are then reclosed by removing thepressure from conduits 40 to 43 through appropriate pressure controlmeans.

In the event of a pressure leak in any of the pillar insulators 7 to 10or interrupters 3 to 6, the blast pressure stored in the pressurereservoirs 11 to 14 will be lost. In the absence of the closures forpassages 16 to 19, it will be apparent that pressure from the remainingpillar insulators and interrupters, as well as from the main pressuresource, will also be lost. Furthermore, where the high pressure gaswithin the pillar insulators is used in part for holding the cooperatingcontacts open when they are moved to their open position, such a failurecould cause the unintentional reclosing of the interrupter contacts. Allof this is prevented by partially closing passages 16 to 19 whereby afailure in any one of the systems will not affect the remaining andisolated systems. Thus, if insulator 7 is broken, the remaininginsulators and pressure containers 12 to 14 will be isolated therefromas will the main pressure source so that a source of blast pressureremains for their respective in terrupters and, furthermore, theircontacts will be retained opened even though the contacts of interrupter3 close because of the failure of its insulator 7.

While the structure described to this point serves the isolatingpurposes required, it is disadvantageous in that during normal operationthere is a substantial pressure decrease in containers 11 to 14 whichmust be quickly restored.

In accordance with the present invention, auxiliary operating means areprovided whereby passages 16 to 19 are momentarily opened during airblast operations so that pressure in chambers 11 to 14 can be quicklyrestored. If, during this momentary operation, there is a leak in anyone of the systems, the gas lost therethrough will be of a negligibleamount because of the relatively short time that the orifice in front ofit is opened.

The novel system includes a two-way valve structure 45 which comprises acylinder 46 having a piston 47 movable therein.

The piston 47 has a stem 48 which carries a valve element 49. Valveelement 49 normally seats against lower orifice 50 by virtue of biasingspring 51 within cylinder 46 which bears on piston 47. Conduit 44 whichcauses interrupter operation is connectable to the main source ofoperating pressure through a valve 52 having a valve member 53 which ismovable upwardly to connect main conduit 15 directly to conduit 44. Afurther extension of conduit 44 introduces pressure below piston 47whereupon valve element 49 is moved upwardly to seal off feeder conduit54. A time delay pressure equalizing means is then provided for piston47 by way of orifice 55 in piston 47. With valve 49 in its lower andnormal position, feeder conduit 54 is normally in communication withconduit 56 and to auxiliary feeders 57, 58, 59 and 60 which producespressure below pistons 24, 25, 26 and 27 respectively.

The operation of the system is as follows:

When the interrupter structures 3, 4, and 6 are closed the control valve52 is in the position shown so that conduit 44 is vented to the externalpressure and conduit 56 and its feeders 57, 58, 59 and 6d are connectedto the pressure within main conduit 15. Thus, the pressure on the bottomof pistons 24 to 27 in combination with the biasing force of springs 36to 39 overcomes the downward pressure applied to the upper surface ofpistons 24 to 27 so that passages 16 to 19 remain substantially sealed.

Accordingly and as described above, each of the auxiliary pressuresystems for each of the interrupters are isolated.

In order to cause the pole which includes interrupters 3 to 6 to open,valve member 53 is either manually or automatically moved upwardly toconnect the relatively high pressure within main conduit 15 to conduit44, whereby the interrupter structures are operated under the influenceof the strong air blast derived from the high pressure air in containers11 to 14. At the same time, a relatively high pressure is placed beneathpiston 47 so that piston 47 moves upwardly whereby valve member 4-9seals olf feeder conduit 54 and vents conduit 56 through opening 50 tothe external atmosphere.

The relatively high pressure on the upper surface of pistons 24 to 27 isthen high enough to overcome the biasing force of springs 36 to 39 sothat these pistons are moved downwardly and the passages 16 to 19 areexposed to the relatively high pressure within main conduit 15 and theauxiliary pressure containers 11 to 14 are replenished.

After a predetermined time, which depends upon the size of orifice 55, asufiicient amount of gas flows from the bottom of piston 47 to the topthereof so that spring 51 can begin to move valve member 49 downwardlyto close off opening 50 and connect conduit 56 to the interior ofconduit 15. At this point, pistons 24 to 27 are moved upwardly to againseal otf passages 16 to 19 and pressure reservoirs 11 to 14 which havebeen restored to their high gas pressure condition.

It is to be noted that if there is a break as in one of the pillarinsulators 7 to 10, that the time that the passages 16 to 19 are openedis relatively short so that there will be only an unsubstantial drainfrom the high pressure source connected to conduit 15. Accordingly, thepresent invention makes it possible to substantially isolate the variousinterrupter structures from the other interrupter structures which areoperated from a common pressure supply while still permitting areplenishing of the auxiliary pressure reservoirs.

In order to initially fill auxiliary pressure containers 11 to 14 withcompressed air when the circuit breaker is put into service or when itis desired to increase the pressure of the auxiliary pressure containers11 to 14, auxiliary means are provided in the auxiliary conduits such asconduit 16 which connect main conduit 15 to the auxiliary pressurecontainers such as container 11. These auxiliary means include auxiliaryconduit 97 having branch feeders 63, 64, 65 and 66 which are connectedto conduit 15 through a cut-off valve 99. Each of feeder conduits 63 to66 are connectible to their respective conduits such as conduit 16through a valve 100, 101, 102 or 103, which is normally closed and isopened when pressure is applied to conduit 97. The valve 99 is thenoperable to a position where it connects conduit 97 to conduit 15 sothat, in the absence of any required operation for the circuit breakerinterrupters or of the valve heads 28 to 31, pressure can be directlyapplied to the auxiliary pressure system. It will be noted that thevalve structure including valves to 103 is required to prevent the flowof gas from the other auxiliary pressure systems when a failure occursin one of them.

A second embodiment of the invention is set forth in FIGURE 2 whereincomponents identical to those of FIGURE 1 have been given the sameidentifying numerals.

It will be noted in FIGURE 2 that the conduit portion 15 which containsthe movable pistons 24 to 27 is shown in a more compact form in contrastto the elongated form of FIGURE 1, although the valve heads and pistonsand springs such as valve head 28, piston 24 and spring 36 serve thesame functions described above. In FIGURE 2, however, the operation ofthe two-way valve 45 for controlling the pressure of conduit 56 isarranged in a difi'erent way.

The two-way valve 45 is normally biased to a position as by biasingspring 51 to permit communication between conduit 56 and conduit 15. Thevalve member 70, however, is movable to an upper position which closesoff this connection and connects conduit 56 to the external atmospherewhereby the pressure on top of pistons 24 to 27 is sufficient to movethe pistons 24 to 27 downwardly to connect the main pressure source totheauxiliary pressure containers such as container 11.

Valve member 70 is controlled by a piston 71 which is movable within acylinder 72 and is connected to valve member 70 through the plunger 74and pivotally mounted beam 75 is connected to piston 71 by link 76. Thepiston 71 is normally biased in its upper position by a spring 73 sothat spring 51 normally holds valve member 7 0 in the lower positionshown.

To control the position of piston 71, the space above in and below itare connected to one another through a conduit 77 which has a controlledbypass therein, including the ball-type back-valve 79. The upper surfaceof piston 71 is connected to conduit 15 by feeder conduits 80 which havea valve 81 connected therein which normally cuts ofi conduit 15 frompiston 71.

As will be seen hereinafter, when the valve member of valve 81 movesupwardly to shut off the space above piston 71 from external atmosphereand to connect the pressure of conduit 15 thereto, piston 71 will movedownwardly to move valve member 70 upwardly and, after a predeterminedtime given by valve 79, the pressure below piston 71 will be relativelyequalized to permit its return to the position shown so that valvemember 70 is reclosed.

The movable element of valve 81 is mechanically connected to gangedpistons 82, 83, 84 and 85 which are movable within their own respectivecylinders.

Each of the poles of the circuit breaker of FIGURE 2, one of which hasbeen described, is provided with a control device which includeselectrically operated valves schematically illustrated as valves 86, 87and 88, respectively. Valve 86 has an outlet 89 which is connected tocontrol conduit 44 of the phase shown in FIGURE 2; while outlets 90 and91 of valves 87 and 88 are connected to similar control conduits of theother two phases.

When valve 86, for example, is energized, the high pressure air ofconduit 15 will be connected to conduit 44 to initiate the operation ofeach of the series connected circuit interrupters such as circuitinterrupter 3 of the phase. These valves further serve to connectconduit 15 to spaces 92, 93 and 94 beneath pistons 82, 83 and 84respectively over auxiliary conduit means as schematically illustrated.

A further auxiliary conduit is connectable to space 95 beneath piston 85through manually controllable valve 96.

The operation of the embodiment of FIGURE 2 may now be considered asfollows:

During contact operation and assuming that the auxiliary pressurecontainers 11 to 14 are filled to their required pressure, when one ofthe phases is actuated as due to a fault signal applied to valves 86, 87and 88, or due to a manually introduced signal to these valves, thevalves open so that the control conduit such as conduit 44 is connectedto conduit 15. Thus, all of the interrupters of the pole are operated.

At the same time, compressed air from conduit 15 is connected in spaces92, 93 and 94 beneath pistons 82, 83 and 84 respectively so that thesepistons move upwardly to open valve 81. This connects the pressure inconduit 15 to the top of piston 71 so that piston 71 moves downwardlyand valve member 70 moves upwardly to vent the pressure in conduit 56.This will cause each of the pistons such as piston 24 to move downwardlyso that the conduits such as conduit 16 are connected to conduit 15 topermit a rapid refill of auxiliary compressed air containers 11 to 14with compressed air from main conduit 15.

After a predetermined time, air flow through valve 79 will causepressure equalization between the upper and lower surfaces of piston 71so that spring 73 can move piston 71 back to the position shown topermit valve 70 to move downwardly to close off conduit 56 and connectit to conduit 15 and thus permit the reclosing of valve heads such asvalve head 28 to isolate the various auxiliary pressure sources.

When the system is initially installed and put into service or thepressure in auxiliary containers such as container 11 has fallen below arequired minimum value, the novel system can cause a replenishing ofpressure to the auxiliary pressure systems without requiring a contactoperation. Thus, the auxiliary valve 96 may be manually operated tocause connection of conduit 15 to space beneath piston 85. This willcause the operation of valve 81 and, as described above, a momentaryopening of the valve heads such as valve head 28 in the absence of anycontact operation.

If the full required pressure is not achieved with this operation, itcan be repeated as often as necessary until a predetermined pressure isachieved for the auxiliary pressure containers.

An interrupter (see FIGURES 3 and 4) consists of a chamber 3 enclosing afixed contact member and a moving contact member 106. The chamber isfitted with a bushing 104 carrying the fixed contact member 105. Inaddition, the interrupter includes sliding contacts 107, which transmitthe current from the moving contact member, as well as a contact spring108, which always tends to maintain the contacts in the closed position.A mechanism 109 is built onto the chamber for operating the contacts andfor opening and closing the channels for the air flow.

The exhaust channel 110 of the chamber is sealed off by a valve disc111, which is actuated by forces in the closing direction clue to thepressure in the chamber. When a breaking impulse is given to the circuitbreaker, the control air conduit 40 is put under pressure. When thepressure in cylinder 112 increases as a result of the inflow ofcompressed air from the control air conduit 40, the piston 113 causesthe valve disc 111 to open at the same time as the seat 114 is put incommunication via the auxiliary valve 115 with the outside atmosphere.This passage remains open as long as pressure is maintained in thecylinder 112.

Since the compressed air is forced to flow through the moving contactmember 106 before passing out through the exhaust channel 110, this willresult in a force counteracting and exceeding that of the contact spring108. The contact member consequently moves in the direction of the airflow until the cone 116 has reached the seat 114. At this juncture, thearc drawn by the contracts is subjected to a combined radial and axialblast of air. Arc extinction then occurs at the first current zero ofthe breaking current.

From the moment when the cylinder 112 is subjected to pressure,compressed air flows through the vent 117 in the piston 113 to the rearof the piston and the valve disc 111 returns to the closed position assoon as the opening force of the piston falls short of the forcesactuating the valve disc in the closing direction. Part of these forcesare now exerted by the cone of the moving contact, which is pressedagainst the seat of the valve disc by the pressure in the chamber. Thisresults in the moving contact following the return motion of the valvedisc so that, when this is completed and the exhaust channel has beenclosed again, it assumes the open position (FIGURE 4).

When a closing impulse is to be given to the circuit breaker, thecontrol air conduit 40 is discharged. The auxiliary valve 115 changesposition without, however,

the piston 113 being affected by the pressure in the cylinder 112dropping to zero. This results in the seat 114 being subjected topressure, and the holding action on the moving contact member ceases.The contact spring 108 then resets the contacts to the closed position.

The chamber 3 is kept continuously under pressure, whereas the controlair conduit 40 is only put under pressure during opening operations. Thecircuit breaker remains in the open position of rest as long as thepressure is maintained, but moves over to the closed position when thecontrol air conduit is being emptied.

In the foregoing the invention has been described only in connectionwith preferred embodiments thereof. Many variations and modifications ofthe principles of the invention within the scope of the descriptionherein are obvious. Accordingly, it is preferred to be bound not by thespecific disclosure herein but only by the appended claims.

I claim:

1. An air pressure control system for an air blast circuit breaker; saidair pressure control system including a source of compressed air, apillar insulator, said air blast circuit breaker including a circuitinterrupting chamber carried on said pillar insulator, a pair ofco-operating contacts enclosed in said chamber, said co-operatingcontacts being operable between a circuit closed and a circuit openedposition, and said chamber being filled with compressed air in theclosed as well as the opened position of said contacts, meanspneumatically connecting said interrupting chamber to said pillarinsulator, meansincluding an orifice pneumatically connecting saidpillar insulator to said source of compressed air; a blocking means forsaid orifice movable between a blocking and an unblocking position,means normally holding said blocking means in said blocking position; acontrol means for said blocking means; means operatively connecting saidcontrol means to said co-operating contacts for operating said contactsbetween said circuit closed and said circuit opened position, saidcontrol means moving said blocking means to said unblocking positionwhen said contacts are operated to said circuit opened position, andthereafter returning said blocking means to said blocking position,whereby said interrupting chamber is momentarily connected through saidpillar insulator to said source of compressed air.

2. In a device as claimed in claim 1, said control means being manuallyoperable to connect said interrupting chamber momentarily through saidpillar insulator to said source of compressed air independently ofoperation of said contacts.

3. In a device as claimed in claim 1, said control means comprising atwo-way valve operable between a first and a second position; saidblocking means including a piston; an air pressure means to maintain anair pressure on said piston to hold said piston in said blockingposition when said two-Way valve is in said first position; movement ofsaid valve to said second position removing said pressure on saidpistons to permit movement of said piston to said unblocking position.

4. In a device as claimed in claim 3, said two-Way valve havingcontrolled leak means for automatically returning said valve to saidfirst position after a predetermined time from the time said valve ismoved to said second position.

5. In a device as claimed in claim 4, said control means being manuallyoperable to connect said interrupting chamber momentarily through saidpillar insulator to said source of compressed air independently ofoperation of said contacts.

6. In a device as claimed in claim 3, said control means being manuallyoperable to connect said interrupting chamber momentarily through saidpillar insulator to said source of compressed air independently ofoperation of said contacts.

References Cited in the file of this patent UNITED STATES PATENTS2,964,605 Schulz Dec. 13, 1960 FOREIGN PATENTS 551,071 Belgium Sept. 29,1956 1,073,578 Germany Jan. 21, 1960

1. AN AIR PRESSURE CONTROL SYSTEM FOR AN AIR BLAST CIRCUIT BREAKER; SAIDAIR PRESSURE CONTROL SYSTEM INCLUDING A SOURCE OF COMPRESSED AIR, APILLAR INSULATOR, SAID AIR BLAST CIRCUIT BREAKER INCLUDING A CIRCUITINTERRUPTING CHAMBER CARRIED ON SAID PILLAR INSULATOR, A PAIR OFCO-OPERATING CONTACTS ENCLOSED IN SAID CHAMBER, SAID CO-OPERATINGCONTACTS BEING OPERABLE BETWEEN A CIRCUIT CLOSED AND A CIRCUIT OPENEDPOSITION, AND SAID CHAMBER BEING FILLED WITH COMPRESSED AIR IN THECLOSED AS WELL AS THE OPENED POSITION OF SAID CONTACTS, MEANSPNEMATICALLY CONNECTING SAID INTERRUPTING CHAMBER TO SAID PILLARINSULATOR, MEANS INCLUDING AN ORIFICE PNEUMATICALLY CONNECTING SAIDPILLAR INSULATOR TO SAID SOURCE OF COMPRESSED AIR; A BLOCKING MEANS FORSAID ORIFICE MOVABLE BETWEEN A BLOCKING AND AN UNBLOCKING POSITION,MEANS NORMALLY HOLDING SAID BLOCKING MEANS IN SAID BLOCKING POSITION; ACONTROL MEANS FOR SAID BLOCKING MEANS; MEANS OPERATIVELY CONNECTING SAIDCONTROL MEANS TO SAID CO-OPERATING CONTACTS FOR OPERATING SAID CONTACTSBETWEEN SAID CIRCUIT CLOSED AND SAID CIRCUIT OPENED POSITION, SAIDCONTROL MEANS MOVING SAID BLOCKING MEANS TO SAID UNBLOCKING POSITIONWHEN SAID CONTACTS ARE OPERATED TO SAID CIRCUIT OPENED POSITION, ANDTHEREAFTER RETURNING SAID BLOCKING MEANS TO SAID BLOCKING POSITION,WHEREBY SAID INTERRUPTING CHAMBER IS MOMENTARILY CONNECTED THROUGH SAIDPILLAR INSULATOR TO SAID SOURCE OF COMPRESSED AIR.